Piezoresistive sensor structures are widely used in measuring pressure or force. The prior art is replete with a number of patents which describe various configurations and methods of fabricating piezoresistive pressure sensing devices. Essentially the assignee herein Kulite Semiconductor Inc. has many patents which describe various type devices. As one will ascertain relatively popular devices are the differential and absolute pressure sensors. A differential pressure sensor employs a differential transducer which provides an output which is the difference between two pressures.
In the particular case of the gage sensor one of these pressures is atmospheric pressure and the other pressure is the pressure to be measured. In this case, the output of the differential transducer is the measured pressure minus atmospheric pressure.
In the absolute pressure transducer, the output is solely indicative of a pressure applied. Thus as indicated above there are many implementations of such transducers and for example, reference is made to U.S. Pat. No. 7,057,247 issued on Jun. 6, 2006 to A. D. Kurtz, et al, the inventor herein, and entitled Combined Absolute Differential Transducer. That patent discloses an absolute differential pressure transducer on a single wafer. In any event and as one can ascertain, an extremely difficult problem in designing absolute pressure transducers is the measurement of the zero pressure.
In zero pressure, the output of the absolute transducer should be zero. In any event, as is the case of most semiconductor elements, the output at zero pressure undesirably changes. These changes are due to temperature, hysteresis, as well as other factors such as slight flaws in manufacturing and so on. Thus, the absolute pressure transducer had to be compensated using various output resistors or using temperature sensitive devices. The compensation of such units at zero pressure required excessive time in order to compensate these devices efficiently and employed additional components which added to the total cost. As one can ascertain, there are many techniques described in the prior art which are employed to compensate pressure transducers for temperature effects as well for hysteresis and other effects. The assignee herein Kulite Semiconductor Products has assigned patents which show vibration compensated pressure sensing assemblies.
Reference is made to U.S. Pat. No. 6,293,154 entitled Vibration Compensated Pressure Sensing Assembly issued on Sep. 25, 2001 to A. D. Kurtz, the inventor herein, and assigned to Kulite Semiconductor Products, Inc. the assignee herein. In that patent there is described a pressure sensing device for producing an output proportional to an applied pressure irrespective of vibration and acceleration of the device. Basically the device uses a first and a second piezoresistive structure which are formed on the same chip. One of the sensors receives a pressure plus a vibration and acceleration while the other device receives only acceleration and vibration. By combining piezoresistors from the first and second device, one obtains an output whereby vibration and acceleration cancel and only pressure is provided. This is an extremely important invention.
In any event, reference is also made to U.S. Pat. No. 7,178,403 issued on Feb. 20, 2007 and invented by A. D. Kurtz, the inventor herein, and commonly assigned. The patent is entitled Transducer Responsive to Pressure, Vibration/Acceleration and Temperature and Methods of Fabricating the Same. Essentially in that patent there is described a device which produces an output proportional to applied pressure irrespective of vibration/acceleration of the device, which device also provides an output proportional only to vibration/acceleration of the device irrespective of the pressure.
It is the intent of the present invention to utilize the devices depicted in the above-noted patents as an absolute transducer and to make the device redundant on a single chip so that a user can obtain extremely accurate measurements of absolute pressure without concern over errors as zero pressure as promulgated by prior art devices.
It is also an intent to provide an improved differential transducer, on a single redundant chip, and to provide a differential and absolute transducer.